With the increase of active population and aging population, the use of a bioimplant for the treatment of both osteo-injury and bone disease has continued to expand. The use of a bone substitute for bone crush and bone removal or the use of supports for embrittled bone require that an artificial bone substitute forms a strong joint or ossifies with the natural bone and therefore ensures structural integrity. When an adjacent structure is porous and is equivalent to bone, the bone grows into the adjacent structure. However, it is considered necessary not only for the bone to grow into the porous structure, but also that there should exist bonding which enables strong adhesion between the natural bone growing into the porous structure and the bioimplant. The bioimplant requires a high strength since it is used in a state of being fixed in the bone, and a stainless steel, a cobalt-chromium alloy and a titanium alloy are mainly used. Ceramics having excellent in vivo corrosion resistance and sliding characteristics, such as alumina and zirconia, and plastics such as ultrahigh molecular weight polyethylene are also used.
An important requirement for fixation of a bioimplant to bone is that the bone grows on and/or into the surface of the bioimplant. Various studies disclose that a calcium phosphate coating on an implant made of cobalt-chromium (Co—Cr) or a titanium (Ti) alloy, for example, a biologic apatite accelerates bone adhesion more quickly than if the implant made of the alloy has a non-coated surface. The biologic apatite Calo(PO4) 6 (OH)2 is one of the main compounds which constitute human bone and teeth. The synthesized hydroxyapatite (HA) closely resembles a natural apatite and thus has been used in a study in which HA is used in dental and orthopedic implants. An implant has been produced which is easily integrated with neighboring bones and tissues by coating with HA or other crystalline calcium phosphates after transplantation.
However, when bacteria are propagated in an artificial joint after an operation of the joint and cause infectious diseases, the infected artificial joint is withdrawn by an operation and the infection is treated with an antibiotic (for several weeks to several months), and then the replacement of the artificial joint is performed. When the prognosis is poor, irremediable problems such as immobilization of a joint and amputation of hands and feet occur.
Therefore, there are proposed a method of coating a hydroxyapatite film having high crystallinity and large specific surface area, which is suited for impregnation with an antibiotic, by precipitating hydroxyapatite on the surface of an implant and drying the hydroxyapatite, and a therapeutic agent-impregnated implant in which the coating film is impregnated with the antibiotic (Published Japanese Translation No. 2005-506879 of the PCT Application).